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Bruhn. Airplane design handbook (100dpi) (T)(817s).djvu |
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Size 24.4Mb Date Jun 22, 2005 |
general, if the torslcnal forces en "he vlng
are snail, thus requiring only a thin covering,
the concentrated flange t/pe of /.'in? structure
should prove the li~ntest...
Cut-outs likewise destroy the continuity of
intermediate interior shear webs of such
sections as illustrated In Figs, (c and 1), and
the shear load in these interrupted webs must
be transferred around the opening by special
bulKh-ads on each side or the cut-out, which
means extra weight...
In general, the
critical flutter speed depends to a great ex-
extent on the torsional rigidity of the wing*
When the mass center of gravity moves aft of the
25 per cent of chord point, the critical flutter
speed decreases, thus it is important to Keep
weight of the wing forward...
The over-all structural arrangement of
members is necessary, but the size or shape of
no individual member is required...
The axial load in each of the 3 stringers has
been replaced by its x, y and z components as
shown on the figure...
The axial load in the
stringers is practically equal to their y com-
component since axial load equals their y force
component divided by the cosine of a small
angle...
A19< 7 Single Spar - Cantilever Wing -
Metal Covered
A single spar cantilever wing with metal
covering is often used particularly In light
commercial or private pilot aircraft...
As the external load is in-
increased the compressive stresses on the thin
sheets starts to buckle the sheet panels and
further resistance decreases rapidly as further
strain continues, or in other words, stress is
not directly proportional to strain when sheet
buckles, Buckling of the skin panels however
does not cause the beam to fail as the stringers
and corner members are lowly stressed compared
to their failing stress...
From equation A) the effective width of
sheet to use *ith each rivet line depends on
the stress In the stringer to which it Is
attached...
The purpose of this simple example problem
was to emphasize to the student that failure of
real aircraft stiffened skin structures occurs
under non-linear stress-strain conditions and
the elastic theory must be modified if fairly
accurate estimates of the failing strength of
a composite structure is to be obtained...
unity is negligible and thus
the normal component can be considered as the
axial load in the stringer...
OF STATION 20
As stated before the engineers In the
applied loads calculation group supply tiie shears
and moments at various spanwise stations...
On
the tension side, the leading edge skin would
be effective in resisting bending axial loads
and thus the moment of Inertia would be slightly
different from that found in example problem 14
Since this problem is only for the purpose of
illustrating the use of the equations, the
leading eage skin /vill be neglected in computing
the bending flexural stresses...
The torque due to the unknown
constant shear flows of qx and qa is equal to
twice the enclosed area of each cell times the
shear flow in that cell, whence
qa = 167 qx + 923 q9
Therefore ZMc g " 167 qL * 923 qa +
* 302796 = 0 (d)
Solving equations (c) ana (d), we obtain,
q^ = -62.3 lb./ln., q, ~ -317 lb./ln...
Each beam portion along these horizontal
strips can be placed together to form the areas
labeled A) to C) in Fig- b of Fig...
This
Interaction curve could be obtained as follows:-
A) Choose a neutral axis direction and Its
location...
Before such
analyses can be made, the size and thickness ot
each structural part must be Known, thus rapid
approximate methods of stress analysis are
desirable In obtaining accurate preliminary
sizes to use in the more rigorous elastic
analysis...
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